The present invention relates generally to apparatus and methods for facilitating wound healing through the use of electrical stimulation, and more particularly to apparatus and methods for providing a voltage gradient and a pattern of current flow that envelopes and permeates the wound.
Connective tissue wound healing typically occurs in three distinct phases. Although these phases intertwine and overlap, each has a specific sequence of events that distinguishes it. During the initial, or inflammatory phase, the body begins to clean away bacteria and initiate hemostasis. The inflammatory phase has three subphases: hemostasis; leukocyte and macrophage migration; and epithelialization. This phase typically lasts for about four days.
The second phase, the proliferative phase, is characterized by a proliferation of fibroblasts, collagen synthesis, granulation, and wound contraction. The proliferative phase typically begins about 48 hours after the wound is inflicted and can extend anywhere from two hours up to a week. In this phase, the fibroblast cells begin the synthesis and deposition of the protein collagen, which will form the main structural matrix for the successful healing of the wound.
In the third phase, the remodeling phase, the collagen production slows. The collagen that is formed in this stage is more highly organized than the collagen formed in the proliferative phase. Eventually, the remodeled collagen increases the tensile strength in the wound and returns the wound to about 80% of the skin""s original strength.
This is the general process that occurs in healthy human beings. Patients that suffer from conditions which limit the flow of blood to the wound site are unfortunately not able to exhibit the normal wound healing process as described. In some patients this process can be halted. Factors that can negatively affect this normal wound healing process include diabetes, impaired circulation, infection, malnutrition, medication, and reduced mobility. Other factors such as traumatic injuries and burns can also impair the natural wound healing process.
Poor circulation, for varying reasons, is the primary cause of chronic wounds such as venous stasis ulcers, diabetic ulcers, and decubitus foot ulcers. Venous stasis ulcers typically form just above the patient""s ankles. The blood flow in this region of the legs in elderly or incapacitated patients can be very sluggish, leading to drying skin cells. These skin cells are thus oxygen starved and poisoned by their own waste products and begin to die. As they do so, they leave behind an open leg wound with an extremely poor chance of healing on its own. Diabetic foot ulcers form below the ankle, in regions of the foot that have very low levels of circulation.
Similarly, decubitus ulcers form when skin is subjected to constant compressive force without movement to allow for blood flow. The lack of blood flow leads to the same degenerative process as described above. Paraplegics and severely immobile elderly patients which lack the ability to toss and turn while in bed are the main candidates for this problem.
Traditional approaches to the care and management of these types of chronic non-healing wounds have included passive techniques that attempt to increase the rate of repair and decrease the rate of tissue destruction. Examples of these techniques include antibiotics, protective wound dressings, removal of mechanical stresses from the affected areas, and the use of various debridement techniques or agents to remove wound exudate and necrotic tissue.
For the most part, these treatment approaches are not very successful. The ulcers can take many months to heal and in some cases they may never heal or they may partially heal only to recur at some later time.
Active approaches have been employed to decrease the healing time and increase the healing rates of these ulcers. These approaches may include surgical treatment as well as alterations to the wound environment. These alterations may include the application of a skin substitute impregnated with specific growth factors or other agents, the use of hyperbaric oxygen treatments, or the use of electrical stimulation. It has also been shown experimentally (both in animal and clinical trials) that specific types of electrical stimulation will alter the wound environment in a positive way so that the normal wound healing process can occur or in some cases occur in an accelerated fashion.
The relationship between direct current electricity and cellular mitosis and cellular growth has become better understood during the latter half of the twentieth century. Weiss, in Weiss, Daryl S., et. al., Electrical Stimulation and Wound Healing, Arch Dermatology, 126:222 (February 1990), points out that living tissues naturally possess direct current electropotentials that regulate, at least in part, the wound healing process. Following tissue damage, a current of injury is generated that is thought to trigger biological repair. This current of injury has been extensively documented in scientific studies. It is believed that this current of injury is instrumental in ensuring that the necessary cells are drawn to the wound location at the appropriate times during the various stages of wound healing. Localized exposure to low levels of electrical current that mimic this naturally occurring current of injury has been shown to enhance the healing of soft tissue wounds in both human subjects and animals. It is thought that these externally applied fields enhance, augment, or take the place of the naturally occurring biological field in the wound environment, thus fostering the wound healing process.
Weiss continues to explain, in a summary of the scientific literature, that intractable ulcers have demonstrated accelerated healing and skin wounds have resurfaced faster and with better tensile properties following exposure to electrical currents. Dayton and Palladino, in Dayton, Paul D., and Palladino, Steven J., Electrical Stimulation of Cutaneous Ulcerationsxe2x80x94A Literature Review, Journal of the American Podiatric Medical Association, 79(7):318 (July 1989), also state that the alteration of cellular activity with externally applied currents can positively or negatively influence the status of a healing tissue, thereby directing the healing process to a desired outcome.
Furthermore, research conducted by Rafael Andino during his graduate tenure at the University of Alabama at Birmingham, also demonstrated that the presence of electrical fields (in this case induced by the application of pulsating electromagnetic fields) dramatically accelerated the healing rates of wounds created in an animal model. This research found that the onset and duration of the first two phases of the wound healing process, the inflammatory and proliferative phases, had been markedly accelerated in the treated wounds while the volume of collagen which had been synthesized by the fibroblasts was also markedly increased in the treated wounds. This resulted in the wounds healing in a much shorter amount of time. Similar findings from other researchers can be found in other wound healing literature.
U.S. Pat. No. 5,433,735 to Zanakis et al. and U.S. Pat. No. 4,982,742 to Claude describe various electro-stimulation apparatus and techniques for facilitating the regeneration and repair of damaged tissue. However, each of these references suffers from the disadvantage that the pattern of current flow generated with these electrode devices does not pass through all portions of the wound and thus, certain portions of the wound site may not be exposed to the beneficial effects of electrostimulation.
U.S. Pat. No. 4,911,688 to Jones describes a wound cover that includes a chamber that encloses fluid around the wound. One electrode is located in the chamber and another electrode is placed away from the wound on the skin. By using conductive liquid within the chamber, a circuit is completed allowing current to flow from the electrode in the chamber, through the liquid, wound, and surrounding tissue and skin to the other electrode. The liquid is introduced into the chamber and replaced using two ports, one port is used to introduce the liquid while at the same time the other port is used to remove the gas (when the wound cover is originally applied to the wound) or fluid within the chamber. This wound cover, however, is complicated to use and involves a delicate process of adding and replacing the conductive liquid.
In view of the foregoing, it is an object of the present invention to provide improved apparatus and methods for easily providing a voltage gradient and a pattern of current flow that envelops and permeates the entire wound site.
This and other objects of the invention are accomplished in accordance with the principles of the present invention by providing an electrode system that includes two electrodes that are adapted for connection to a power source sufficient to cause a current to flow between them. The electrodes are shaped and oriented to cause a pattern of current flow that envelops and permeates the entire wound site. Such shapes and orientations may include a circular first electrode located at and covering the wound site and a second electrode shaped as a ring fully encircling the first electrode. The second electrode may be located outside or partially within the wound site. Other suitable shapes of the electrodes may include electrodes that are ovally shaped, rectangularly shaped, triangularly shaped or any other suitable shape where one electrode encircles the other electrode. The shape of the electrode may conform to the shape of the wound.
The two electrodes of the electrode system may be mounted to an oxygen-permeable top layer that is impermeable to water and water vapor. The top layer may provide support for the electrodes and may allow the wound site to breathe.
The electrode system may also include an electrically insulative element that is disposed between the two electrodes. The insulative element may ensure that most if not all of the current flow between the electrodes passes through the damaged and healthy surrounding tissue.
The power supply for applying a voltage potential across the electrodes may be local to or remote from the electrode system. In one suitable arrangement, the power supply is attached to the top layer of the electrode system. The power supply can be configured to provide a constant or varying voltage, a constant or varying current, or any other suitable electrical output to the electrodes to facilitate wound healing. For example, the power supply may be configured to provide the desired current or voltage to the electrodes at different time intervals with the same electrode system in place. In one suitable embodiment, the power supply is a battery. In another suitable embodiment, the power supply is electronic circuitry that is configured to provide the desired current or voltage.
In another suitable embodiment of the invention, the two electrodes of the electrode system are comprised of oppositely charged polymers of sufficient voltage differential and charge capacity to cause a current to flow from the first electrode to the second electrode through the wound.
The electrode system can be designed and fabricated to be either disposable or reusable.
The electrode system according to the various embodiments described herein is capable of generating a voltage gradient and a pattern of current flow that envelops and permeates the entire wound site. Such a pattern of current flow maximizes the recruitment of the necessary cells to the wound location at the appropriate times during the various stages of wound healing.